The Global Positioning System (GPS) is a medium-range circular-orbit satellite system, it provides accurate locating services for most of areas on the Earth. GPS was originally developed for military purposes. GPS is currently available to civilians and has brought about revolutionary changes in daily life. For example, through signals provided by GPS and an e-map provided by a locating/navigating device, vehicle drivers are able to locate their own positions, to know where they are and to enjoy the navigation function.
However, since a vehicle is an object that may move at any time, GPS signals are likely to be attenuated or shielded as the vehicle passing by a building, through a tunnel or to be sheltered by the terrain. If the locating/navigation apparatus disposed on the vehicle fails to receive the GPS signals, it will fail to locate and to provide the current vehicle location, so that the locating/navigation apparatus can not provide the navigation function.
To continuously indicate the current vehicle location as driving in an area that the locating/navigation apparatus can not receive GPS signals, a sensing unit for sensing a plurality of parameters has been provided in the prior art to solve such a problem. More specifically, according to the parameters sensed by the sensing unit (e.g., an accelerometer and/or a gyroscope), the locating/navigation apparatus can estimate the current vehicle location by employing a dead reckoning approach from a previous location obtained before failure of the locating/navigation apparatus to receive GPS signals. In this way, the locating/navigation apparatus can keep presenting the current vehicle location even when it fails to receive GPS signals.
Unfortunately, the location accuracy of the locating/navigation apparatus may decline because these parameters sensed by the sensing unit are affected by various factors. For example, when the vehicle is driving on an uphill or downhill road, the parameters sensed by the sensing unit are erroneous due to influence of the gravity. Besides, the dead reckoning approach adopted by the locating/navigation apparatus is only able to estimate locations of the vehicle in a plane. However, there are transportation network formed of planar roads and elevated roads in modern cities, employing the dead reckoning approach will cause significant degradation in location accuracy of the locating/navigation apparatus.
In view of this, there remains a continuing need to provide locating/navigation apparatus with a more accurate locating method that can inform users of their current location even when GPS signals are not available.